Various processes and apparatus are known in the prior art for refrigerating or freezing products, including hardware and foodstuffs. Many of these systems utilize liquid cryogen-chilled refrigerating gas. Typically, the prior art systems attempt to vaporize the liquid cryogen substantially before contact with the product to be refrigerated or frozen, but in many instances the cryogen does not become a fully vaporized and, in fact, collects, pools or settles on various horizontal surfaces in these known prior art refrigerating or freezing systems.
Exemplary of such a prior art cryogenic freezer is the freezer disclosed in U.S. Pat. No. 4,475,351, wherein a cryogenic liquid refrigerant is sprayed into one or more of the cooling zones in the central region of the tunnel comprising the freezing in an upward direction into the rotating fans of the freezer to thus vaporize the refrigerant before it flows downwardly into contact with conveyed products passing through the freezer. The suggested liquid cryogen is liquefied nitrogen. Other cryogenic liquids such as liquid carbon dioxide, liquid air and refrigerants having normal boiling points substantially below -50.degree. F. (-46.degree. C.) can be used. The system is designed to utilize cryogen in a manner so that it does not directly contact the food product in its liquid state in order to avoid thermal shock if the product was directly exposed to the cryogen spray. However, merely directing the liquid cryogen into the recirculating fan does not insure that essentially all liquid cryogen is evaporated prior to contacting the product or horizontal surfaces where the cryogen might pool.
U.S. Pat. No. 4,481,780 discloses a process and apparatus for the generation of a cold gas by mixing a liquid cryogen and a relatively warm gas together in a double T-shaped conduit apparatus whereby when the warm gas and the cryogen are mixed, total vaporization of the cryogen occurs without pressure fluctuations or pulsations in the mixing area. The system requires a reservoir or dead-end 6 in order to ensure that cryogen is fully vaporized before leaving through the outlet 8. The drawback of this system is that it requires a discrete premixing zone prior to the utilization of the chilled coolant gas.
U.S. Pat. No. 4,524,548 discloses a product cooling apparatus for deflashing molded products by embrittleing the flashing of the products and blasting it with solid particulate material. This system also attempts to avoid contact of liquid cryogen and the product being deflashed in order to preclude thermal shock to the deflashing product. Liquid cryoen evaporation is achieved in part by locating the liquid cryogen entry sufficiently away from the product site and in a dispersal direction sufficiently away from the product so that the cryogen only contacts the product after circuitous entry into the product chilling zone. The cryogen is assisted in its evaporation by co-mingling with particulate material that is thrown against the product to remove embrittled flashing.
Other patents directed to refrigeration, refrigeration with cold air and refrigeration with liquid air, as well as freezing processes and apparatus, include U.S. Pat. Nos. 2,447,249; 3,733,848; 3,868,827; 4,033,140; 4,229,947 and 4,315,409.
The drawbacks of the prior art in refrigerating and freezing of products and foodstuffs, particularly using liquid cryogen, such as liquid air, which presents special problems in addition to the thermal shock effect of known prior art liquid cryogens are overcome by the present invention as described below.